Based on geographic information system (GIS) and geostatistical analysis, this paper studied the spatial structure of Aphis gossipii Glover population in Xiangshan District of Zhongwei City, Ningxia Province, with the spatial distribution of the population simulated by ordinary Kriging interpretation. The spatial structure of A. gossipii population varied with its occurrence stage (initial, blossom, and final stage). The semivariograms of A. gossipii could be described by exponential or Gaussian model, indicating that A. gossipii had an aggregated spatial arrangement. The aggregation degrees at different occurrence stages were all beyond 45%, and the spatial correlation ranged from 10.37 km to 29.11 km. The spatial variance was greatly affected by spatial autocorrelation. The population dynamics of A. gossipii at its different occurrence stages could be easily analyzed and intuitively simulated from the two aspects of time and space by spatial distribution simulation, and thus, the occurrence position and degree of A. gossipii could be easily determined.
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A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the determination of five pyrrolizidine alkaloids (PAs) (monocrotaline, senkirkine, retrorsine, seneciphylline and senecionine) in honey. The honey samples were dissolved in 0.1 mol/L hydrochloric acid solution and a strong-cation exchange column was used to purify and concentrate the target analytes. The separation of the analytes was carried out on a Phenomenex C18 column (100 mm x 4.6 mm, 2.6 microm) using the mobile phases of acetonitrile and 5 mmol/L ammonium acetate-0.1% (volume percentage) formic acid aqueous solution with gradient elution. The separated compounds were detected in multiple reaction monitoring (MRM) mode via positive electrospray ionization (ESI+). The calibration curves were of good linearity in the range of 1-100 microg/L (r > 0.99). The limit of quantification of the method was 1.0 microg/kg. The average recoveries were between 73.1% to 107.1% at three spiked levels (1, 20 and 50 microg/kg) with the relative standard deviations (RSDs) in the range of 4.1% to 17.0%. The proposed method was applied to different kinds of honey from China, New Zealand, Spain and Australia. The samples included rape, vitex, sunflower, cotton, tilia tree, date, acacia, buckwheat, manuka and eucalyptus honey. Monocrotaline, senkirkine and retrorsine were not detected in the collected honey samples. However, seneciphylline and senecionine were found in most of the honey samples. The concentrations of seneciphylline and senecionine were 11.0 -31.1 microg/kg and 8.3-29.1 microg/kg, respectively.
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